The characterization and inheritance of chromosomal variation in Glomerella graminicola.

摘要

The purpose of this study was to establish karyotypes and study chromosomal variability in isolates of the phytopathogenic fungus Glomerella graminicola. The karyotypes of six G. graminicola isolates were established using pulsed-field gel electrophoresis (PFGE). Although overall characteristics of karyotype organization in the examined isolates were conserved, all isolates had unique karyotypes and contained two classes of chromosomes: maxi-chromosomes (3.1 to {dollar}sim{dollar}8Mb) and mini-chromosomes (476 kb to 1.2 Mb). Southern hybridization analysis revealed that mini-chromosomes contained unique sequences including expressed genes, and that sequence homologies were shared among mini-chromosomes in different isolates but not among mini-chromosomes within a single isolate. Sequence deletions and rearrangements were demonstrated to be responsible for some of the observed mini-chromosome polymorphisms. Analysis of electrophoretic karyotypes from tetrad progeny recovered from crosses between parents with different karyotypes revealed that meiosis generates karyotype variation. This variation was attributed to reassortment of polymorphic, parental chromosomes, premeiotic loss of sequences, and generation of novel-sized recombinant chromosomes. Based on these data, I conclude that mini-chromosomes are integral, genetically functional components of the G. graminicola genome and that the observed chromosomal variations are not effective barriers to meiotic transmission of polymorphic chromosomes.